Gitlab + Mattermost on Ubuntu 16.04

Use ports and a second domain name we have full control over to get around not being able to install mattermost in a subdirectory

Solve an annoying “Failed to upgrade websocket connection” error in Mattermost that means it doesn’t have real-time services

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Specifically, we have two domain names.
a) organizational-domain.com (in our case, a .edu domain), which all our files will be created on
and
b) your-domain.com (in our case, a domain we registered separately through godaddy)

To resolve that we a) cannot create subdomains on the organizational domain, and b) must install mattermost on a subdomain, not a subdirectory, we will create subdomains on your-domain.com and point them to ports on the organizational domain

Install Gitlab Omnibus, Community Edition, for the first time
(Note: Omnibus i think just refers to the official latest and greatest gitlab release)
0a. Add gitlab repository as per https://about.gitlab.com/downloads/#ubuntu1604
0b. sudo apt-get install gitlab-ce

$ nc -l 8001
( you should see
nc: Address already in use
Else, you’ll see nothing)

If the port is open and not firewalled, you should be able to talk to yourself
In tab one: $ nc -l 8002
In tab two: $ nc organizational-domain.com 8002
Whatever you type in one tab should show up in the other